This invention relates to a process for producing aromatic polyester fibers having high strength and a high modulus of elasticity by melt spinning with stable operation for a long period of time.
Recently, it has been disclosed that aromatic polyesters showing optical anisotropy in the molten state can form fibers having high strength and a high modulus of elasticity by melt spinning. Melt spinning has many advantages in that no solvent is used and, conventional spinning apparatus can be employed. But aromatic polyesters, which can yield fibers having high strength and a high modulus of elasticity by spinning, readily decompose during spinning or generate bubbles by reactions such as polymerization, crosslinking, etc., due to the high spinning temperature.
Aromatic polyesters showing optical anisotropy in the molten state, unlike conventional polyesters, nylons, etc., have a softening temperature and a melting temperature very close each to other and a large temperature dependence of the viscosity of the melt so that rapid melting of the resins takes place at the melting portion in a screw type extruder to produce a melt having a very low viscosity. Thus, it is very difficult to deaerate in the molten state, which results in making it impossible to spin continuously a long period of time.
Heretofore, there have been proposed various processes for melt spinning aromatic polyesters showing optical anisotropy in the molten state (e.g. Japanese Patent Examined Publication No. 482/80), but these processes, as exemplified, were carried out only on a small scale at a laboratory stage. Therefore, development of a process for the stable melt spinning of the aromatic polyesters showing anisotropy has been desired.